Mechanism for eliminating overstrain of measuring spindles in machine tools



' March 24, 1931. F. TURRETTINI MECHANISM FOR ELIMINATING OVERSTRAIN'OF MEASURING SPINDLES IN MACHI NE TOOLS Filed May 25. 1929 jig-I h o In! l i I l l I 2 H k" II J LL ll.

BY wax/ ATTORNEYS.

Patented Mar. 24, 1931 UNITED STATES FERNANIJ TURRE'ITINI, F COLOGNY-GENEVA, SWITZERLAND, ASSIGNOR TO THE FIRM SOGIETE GENEVOISE DINSTBUMENTS DE PHYSIQUE, OF GENEVA, SWITZERLAND MECHANISM FOR ELIMINATING OVERSTRAIN' 0F MEASURING SIPINDLES IN MACHINE,

PATENT. oFF lcE TOOLS Application filed May 23, 1929, Serial No. 365,532, and in Switzerland October. 13, 1928.

p In a large number of machine tools, in particular on lathes,milling machines or boring machines, the following arrangement is found. 1

The work table or the tool Carrying slide is moved by a screw which at the same time has to serve as measuring member. The

screw on these machines visfrequently pro-- vided with a divided circle serving for measuring the amplitude of the displacement which the action of the screw produces.

This arrangement cannot give a guarantee of accurate measurements because the screw which has to move the heavy and resisting slide and at the same time overcome the reaction of the cutting edge of the tool is subjected to wear which is much too rapid.

The object of the present invention is to remove this disadvantage. The invention is characterized by two screws for which the slide block acts as a nut and one of which is adapted to drive this slide block and the other to measure this displacement, by means of a movement transmitting mechanism which is placed between these screws and which is arranged in such a way that it only actuates.

the measuring screwwith a torque which is small enough to avoid every overstraining and wear of the measuring screw.

This arrangement, which implies a division of the-functions of movement and measuring, permits the measuring screw to be removed from the eifects of wear.

The accompanying drawing illustrates a form of construction of the subject of the invention byway of example.

' Fig. 1 is a plan'view with a section taken along the line II in Fig, 2.. r r

Fig. 2 is a section along the line I III in Fig.1.,' I In this form of construction the slide block is formed by 'a work table a of a machine tool, which table has to move on a slide bed 6. 0

is. the driving screw which has to support the whole of the necessary effort employed for movingthe table a. d is a measuring screw provided with a graduated head 6 upon whlch canbe read the rotation eifected by the screw d. r and s are the nuts connecting the screws to the table a.

The two screws cfand dare coupled together by the following i mechanism. A

toothed wheel h is loosely mounted upon the screw 0 but its relative movement with respect to the screw 0 is limited by a finger i rigid with h which is adapted to move between the two faces j of a recess formed in the sleeve is keyed upon the screw c.- The toothed wheel it will thus only drive the screw 0 after its driver i has travelled over the space provided intentionally between the two opposite faces j of the recess formed in the sleeve 70. I

Zis a toothed wheel engaging with h mounted without keys upon the screw 03 andwhich has to transmit movement to the latter through the medium of a connection limiting the couple which can be transmitted from the wheel h to the screw 05.. This connection is constructed in the form of a friction coupling formed by two plates m and m keyed upon the screw (Z but movable axially upon this screw and holding between them theiwheel Zunder the pressure of springs n. The torque transmitted by this friction device can be so small that no stresses able to produce wear of the measuring screw (Z can occur.

The pinionh is moved by a pinion p itself actuated by a crank 9. Instead of this hand controlling device, the screws can be actuated by any mechanical feed device.

When the crank q is turned the pinion p transmits its rotation to the pinion. hand through the latter instantaneously to the screw d by means of the pinion Z frictionally coupled to this screw, the effect of which is to bring the threads of the screw dinto contact with those of the nut 7'. In fact the torque which the friction coupling-can transtion coupling so that the screw (Z is allowed to commence to turn and thus follows the movement of the table a.

In this way the lead screw 0 is arranged to withstand the whole effort required for moving the table a and the measuring screwd only undergoes the action of a very small torque which is nevertheless just sufficient to ensure the measuring contact on the flanks of the threads of this screw against the flanks of the threads in the nut 1" rigid with the table a.

,In .this' way vany 'mechanical fatigue of the screw d is avoided and the latter simply serves as a measuring screw and preserves its accuracy because it is removed from the effect of the wear which would be produced it a re sistance hadto be overcome;

-With a view to eliminating the eifect of possible differences in the pitches of the screws c'and (Z 'or in the accuracy of the wheels Z and hfwhich differences will be detrimental to the good working of the arjrangement, the transmission ratio of the I wheels] and h and the respective value of the pitches of the screws 0 and (Z may be combined intentionally in such a way that f the nut r is moved alone by the screw (Z it I will move a little more rapidlythan the nut "from'that shown at p and q in the figure,

provided thistorque limitation device can operate for both directions of rotation. V I claim:

"1. A device for producing the movement of a member on a machine tool and for meas- 'uri'ng' this movement, comprising a fir t screw for moving the member, a second screw for measuring the displacement of the member, nutsformed on'said member and engaging with the two screws, and a'toothe'd wheel loosely mounted on the driving screw, a sleeve keyed on said screw and hav ng a recess iformedf in it, one or several driving members 'OIl SElI'Cl toothed wheel engaging in said recess and'forming a lost motion driving'means for said screw, a second toothed wheel freely rotatable on the measuring screw and engaging fthe toothed'wheel on the driving screw,fricti'on' plates slidably and nonrotatably mountedon the measuring screw and'held in'resilient engagement with said second toothed wheel, the resilient frictional pressure being such that slip is produced when the resistance to rotation of the measuring screw islarger than that practicallyadmissible for a very on the. member andengaging with iitheltwo screws, a gear carried on said firstscrew,

driving means for actuating said gear and thereby rotating said first screw, a second gear operable to rotate said second screw; and a yielding connection between saidtwo' gears whereby a fraction only of the "torque imparted to said first mentioned 'gear'is' transmitted to said second screw.

3. Adevice for producing'the movement of a movable member'ona machinetoola'nd for measuring the displacement of'the member, comprising a firstscrew for moving'the member, a second screw "for measuring the displacement of the member,'nuts formed on the member and engaging'with'the'two screws, a gear carried on said first screw, driving means for 'actuating'said 'gearand thereby rotating saidfirst screw, a second gear operable torotate said second screw, and a yielding connectionbetween said" two gears whereby afraction only of the torque imparted to saidfirst mentioned'gear is transmitted to said second screw, and alost motion connection between said first mentioned gear and the first screw whereby'the drive is transmitted to this first screw with a certain lag with respect to that of the second screw.

4. A device for producingthe movement of a movable member on amachine tool and for measuring the displacement of the member, comprising afirst screw for moving the member, a second s'crew' for measuring the displacement of the member, nuts formed on theflmember and engagingwith thetwo screws,'a gear carried on said {first screw, driving means for actuating'said gear and therebyrotating said first screw, a second gear operable to rotate said second screw, and a yielding connection between s'aiditwo gears whereby a fraction-only of the torque imparted to said first mentioned gearis transmitted to said second screw, the transmission ratio of the connection between said'two gears. and that ofthe pitches of the'two screws being so chosen that if the movable member were moved by the second screw alone it would move a little more rapidly than it is'moved by thefirst-screw.

-5. A device for producing the movement of a movable member on a machine tool andfor measuring the displacement of the' member, comprising a first screw for moving thememher, a second screw for measuring the displacement of the member, nuts formed on the member and'engaging with the two screw-s, a gear carried on said first screw, driving means for actuating said gear and thereby rotating said first screw, a second gear operable to rotate said second screw, and a yielding connection between said two gears whereby a fraction only of the torque imparted to said first mentioned gear is transmitted to said.

second screw, a lost motion connection between said first mentioned gear and the first screw whereby the drive is transmitted to this first screw with a certain lag with respect to that of the second screw, and the transmission ratio of the connection between said two gears and that of the pitches of the two screws being so chosen that if the movable member were moved by the second screw alone it would move a little more rapidly than it is moved by the first screw.

6. In a device for producing the movement of a movable member on a machine tool and for measuring the displacement of this member, the combination with a stationary supportin member for said movable member, of a rst screw for moving the movable member, a second screw for measuring the movement of this member, said two screws being journalled in one of saidmembers, nuts formed on the other of said members and engaging with the two screws, a gear carried on said first screw, driving means for actuating said gear and thereby rotating said first screw, a second gear operable to rotate said second screw, and a yielding connection between said two gears whereby a fraction only of the torque imparted to said first mentioned gear is transmitted to as said second screw.

In testimony whereof I aifix my signature.

FERNAND TURRETTINI. 

